Traditionally, environmental condition sensors utilize effects of the environment which induced a voltage or current changes in a circuit to cause electrical changes which are usually measured in the form of a readable or recordable mechanical deflection. Some of these systems are bulky and relatively insensitive to the conditions for which they are intended.
There is an increasing interest in the use of optics for sensing acoustic waves, temperature changes, acceleration and ac magnetic fields, as well as other environmental conditions. In each case, the sensor must be sensitive to the field or condition to be sensed or measured, while at the same time it must be insensitive to unwanted perturbations. Recently, there has been considerable interest in sensors employing single mode optical fibers arranged in the form of a Mach-Zehnder interferometer wherein the incident field or condition to be sensed or detected induces a phase modulation in light passing through different arms thereof. This is more fully discussed in Measurements of Small Phase Shifts Using a Single Mode Optical Fiber Interferometer, Opt. Lett., 1980, 5 pp. 139-141. Other approaches using optical fibers rely on intensity modulation transduction mechanicians. See, for example, the article by Schilieren entitled Multimode Fibre-Optic Hydrophone, Appl. Phys. Lett. 1980, 37, pp. 145-147.